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POPULAR E LE CTR ONI CS M I-DVM

HIGH-QUALITY, LOW-COST

MINIATURE DIGITAL VOLTOHMMETER

This is an up - traded version of e origin'l Popular

tonks "w · Cost D ia i ul Vo l tohmmete r" th.t ap

peared In our December 198 i JI , Asembly tn

bltn ud, atcur.J .nd stability i mproved , and the

in str u ment may b. constructed for I dollar outla , of

les than he 1968 proto t ype . Deta il e d specifications

.ppur on paa' 4 5 . fulll5embly det.ils If. published

in this I u e .

\'ollohmmctcr wilh 1% Hccurncy that elm be

built for nbout lIle cost of \ better-grade

:lnalO; multhneter. It uss 2%.(i<'I\{\c Xixic

tube 1lI11l1'rie l1i"pla\' to illditnlc-brightly

:ulll lIIUUllbi:"1I0U.�I,'·-:IIY d.e. voltage from

10 millivolL; to 200 "olts or any resistnnce

v a l u e from 1 to 200,000 olnns. H hilS intemal

.�eJf'-c·nlibrntioli nnd 7'I'Oill;.

The \Iini-DV.\l 'nn be 1""�ell1bled in its own

tl';: 01' Ille inlcl'llf\l ct�tronics cnn be used:ls

a O·HJ) di-ilnt counter or J)nncl meter to indi

cate digitnlly :Illy qU:lIltily thnl cnn be con·

,-crl} inlo n 0-2-"0It d,c. sigllal driving \

I-mgohm load. Complete I:llllic ' al ;peciien.

tions nrc given in the Tnble. 'J'hc instllcllt

consists of 1\ countcr modulc, 11 powcr mod

ule, nllli somc c(I.C-moulltti cOlilrols nnd

cOlllponcnts.

IT l$"T o,"rEN lhnt you sec n smnH.

compact. digitnl ,"ollohmmct!r wilh Kixi�

tube rendout Ihnt doesn't cost nt lea"t several

hU(lr'oo dolluli. '1'110 ".Uini-DV1U' dcscl'ilJc<l

here I; n SC\'CIl-rnn.C, high-impl<lnncc digital

========== COVER STORY BY DON LANCASTER

Septembe,.1970

A SS EMBLING THE

.. n

�

2.7(

ZERO

••

*O � . " ".

IN4154

*o NOT lIU8STITUT[

1.5(

n t ed cil'<;uit ho<\nl i. csCnl ial (or

this module. Yon \'nn plln·II'I.�(, "nc liS 111'11-

lionetl in the PurL,; l,i�tor yOIl ('nll llwkc ."UIlI'

OWII using the ch·\,in; guide .1IuII"1I in Fi-. 2

ami the Ilrillin, illsindiolls ill Fi'. a.

In layill� out tile compollCIlL; as ,11<,wII ill

Fig. 4, mnkc ,-;l1rc that lhe jUIllPC'I . " (#2.

.... L

Xotu PM'li'-III"rl)" till' oricnhltiOIl oe the

s('mi,·OIHill(;tUn< .•

[iode;, IC's, etc. There nc

llU.c.l dilTcrclit killd.� uf bH.�ill> iu\'olvcd 011

the tnHlsislurs ll.�C<J. All tran;isto'.� "point"

the smne "·II .V, e�(''pt tOI" Qu. 'l'llclC's nrc

i,lclltilic.l b.l· " Ilot and lltlt:1I. Xul.e that 105

POPULAR ElECTRONICS

IN,3�

OFFSET

Counter Module Construction. The

stiuom;,tic of the 1;01l1l\Cr module i; ;huII"1l in

o'i;. ]. A p ri

wires) an' l)ositiO)u('.\ cXlletl,1' as shown and

lhat insu l ate,l "lee"in; is u;cd 11"\101'0 it is

IlP(·d

PARTS LIST

COUNTER MODULE

! ! !

C 1-J'/'I'F, 50·volt Mr1lr ClJucilOr

C2-/J·fJF p"lysl)"rcnc or miw CUl'ucjlo,

CtAO·00·I'F /!olp/)'rIIC Or mle< CupacilQr

115 neLIlcd (see /ext)

CJ-IOO·p.F, SO·volr c/cclrolr1ic CllllcilOr

CoI-I-p}', 10·,"011 dec/,o/rlie capacitQr

C5<J.OO5·",F disc ceramic cupucilOr

C-}.I·IIF, lO·voi{ disc cuulllic calcilnr

DI,06-1""/7.3I 5.j.>:o/t zener diode (dQ not

su/""illlie J I)

D2.03j)S-Silicon com/,uler diode (IN914

or simi/ar)

1-27"'0/1. /-IllI =cner {/N47} or simi/a')

fel-Qm"l IIro·i,l/mt glllc (f% rJ/u MG·

7241')

fC2,IC.Jenllic counter (MQtorola MC780P)

!C-I-Duol JK Fli/rj/op (Motorola MC791P)

/C5,fC-Lllu··k�cl 1/10 decoder (M"lor,,11l

MC770I')

QI-TmnsiSlor (/O/lrll/O .1"56521, tEo not

.�ul$l;IUIe)

Q2-TransislOr (MolOro/< MP56523, do not

slIh."illll:)

QJ.Q6-TnmliMoT (Ml/oro/a MPS2923 Or

2N292.1)

Q7-Tnlll$i�lor (Tcu /nllfumenl$ TIS43, do

1Iol.,ubsrilulej

Q8.Q29-Twnsillor (Sprague 2N3877, do nol

.ubslilllte)

UI-IO·mcgohm

N3-3.3·megohm

U---8.,h",

R5-27(l·<>hlll

R6-MO.Q·oh",

R7-IOO)·ohm

RB,fl23,UU.R27-33jJOO·ohm

R9,R2047((}.ohm

RI0,R21.R22-8QO·ohm

RII-J30·ohm

1l17-J3()·ohm

l 18.1l8.R29-IOOO·oh m

RI9-12.ohm

R25,R26-6BjJOO.oh III

)JOJl

R I6

2�Ol

OiM S

, . v

: IN914 ::::

;..�" - 0 .

IN41H

I�F

•

, )

I, 5

] I

COUNT

+J.6V

RESET

All resistors

34·rmu

2N2923

'' '

" "

I ' " -,

,�, ,

UN8AH K

•

R2-IO.ooo·ohm, 'e·mounl /inc.r I'olenli.

"lIleler

UI2565,ooo·ohm, 1% weci!ion resislOT

l 13-«JAOO·ohm. 10 wccision rcsistor

R /1-59OO·"hm, 1% {recision rcsistor

� 15590·ohm, 1% lTcdsion resistor

{ 16-2)·ohm, Pe·mOIWl linellr IlQlenliometeT

YI,Y2-Ni.rie t .. be (8l1rrQlIglis 8-5750)

Yl-Neoll /wlb (Signl/ite A·261)

Misc-Printcd circuit terminuls (21, Oillion.

Ill); #21 solid rrire for jllll/pers; ill$uit.tcd

sIeelling; snap·in mounting SlllcelS (8);

solder: eiC.

Note-The 'olloll'in; s (wail/lblc from Soulh.

meS! Te<:hnicul PrOlh'Cls, Box 16297, Sail

Alltonio, TX 78216: etched/lld drillcd PC

bOlmi, $6.75, JOsl/Hlid, inSllTlllee extra.

, . ' "

0.4( 1,,( '''A

, " �n

I UL

rind lOG go in "upsidc down" with l;;pcet to

101-104. AlO, be carcful not to mix up tlrc

two calibration potentiomctcrs, R2 and (16.

Thc lI'a.rning, "Do Not Substitutc," 011 somc

part� ill the Pa; I.ist �hol1ll he obscn'c<l

�incc subtlc (·hnngc; in pcrformnn(C mn.\· rc

suI. frolll apparcntly rcasonablc aitcl'llu l irc i ; .

Usc n 10w."'nHngc soldcring iron and finc

soldcr to iustall nIl componcnts.

Fig. L The schematic has been broken inlO

two pars. This section con l a ln s the volt·

age·la-frequency converter, the reset and

unblanking circuit, and the ohms constant·

current source. Circuit conlinued o ve rl e af.

September, 1970

--,"

CPt

+lICV

IliMT

CENTE'

. . IK "

I�7!10

' .

! I

1 �

• r

. �I. \

010 011 Oil 013 014 Ol�

- -

- :; -: ) :

� )

-�

M :

....

- - - - _ .... :

l �)

- -- - -- --- ---- - ---

1 l �)

�

T . ) '

The second half of the circuit

contains the units, tens, 1, and

overrange indicators. Only the

units decade is shown in detail

as the tens decade is similar.

The overrange indicator is c an ·

nected to terminal marked ··X".

010 011 Oil 013 011 015

l��

.. "

5,H, +"

, , 6

, , • I GNO " " y.

DECODE"

' "

MCT70p

��

Ji ,

1 1 , 1

12 � nt l -

" 1

C l

, 1 1

, ,

14 13

, IST " 2 4 I

itO m

MCTIO.

�

�"I

TTl

UNITS

that pl�lgres.;i\'ely siiortci' kat!" "nn llf' in

serted 1"0:lt n t i m e u11tillllc i11be .� �eafe,l .

Be Nlrcfll1 10 havc bolh �ixie lubc . ; \'prli"HI

1\'llen .'01 Iinall.l · Shlder 1111'1ll in plnce, .\ I�,) e

�l1n' tlmt tile tnbe lenol.. nre pnlled alllllc way

jhl·"n:.:h the PC honnl: a lw11t or ;IIOl"lil1g

I,'a,l in.�ille tile pl:l..�ti(· insertion "lIi;le "all be

"pry ,1ifliclI!t to fix nfter tllC ll1be i . .; .;fJld!l"e/!

Power Module Construction. 'I'll!' (lUn

POPULAR ElECTRONICS

--- - -- -----

'fhc �ixic inrli(:ntor.� Illl' . '· be mOlllll',] ei1l1l'1"

using the p]n�li.· b,\�ing" g11ide:1� 1111 in�{'rliOIl

ahl: or tllC ICH,ls mHr IX' ,'111 ,lia:!tJllally �('

in pine!.

+ •• 6 I

' "

LEFT

l�

7 •• �

OP.' •• "ecp

He •• �

, •• 2

O •• 1

, . '"

'" '"

'11,'12

eOTOM

VIEW

" . '" ""

- '

. " . " '"

, ,

U�8 . K

•

'" I

: � :o

.,r�:..

" .

�

' I I

" " 12 II g 9 ,

I � � j

•

791P .i.

2 3 4

5 6

I I

--)

• 5 6 7

TENS

IeI' module l([ui"c.� 3.6 ,·olt; <1l-tOO ll.\, 180

\·oll.� at : ) \ and 30 volts ilL J:l m.\ for

p0lI'er. Th..-;c :'C Jl!'o\'idl�1 by tile PVWCI'

module whicll i� ll'inm h,l' a power trllll"funn_

cr, Tile pow!'!" module (sec Fig. 5) hl\.�:1 full.

wave ccntcr-l:11'PCt! [ , C(·\ificI' for Ille hi;!1

with 30 \"nlts Jcril'cd tllnIIgh \ dl'uppill; rl!

sistol'. Waldl the i1i(�lc poinri!)': nth\. if ,Ii(

fCI'Cut bt'Cnk,IOlI"tI wlila-c 1'1ltillg� at'C 11�C(1 1'''1'

tlie low-\"oltn;c diod(��, he snrc Iot to inler

dlflngc them.

\Vhilc a prinlCd l ' i rc u i l 01<\ is nol ."'-�CI1-

tinl fill" the p<l\\"('1" rno,lule. iL is ("oll\{'uienL

'""!tnz/' ln! n silllilnr Ollt! for li l e lOll" ,dln:' ,

Seprember, 1970

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